The "interpreter-based threads" provided by Perl are not the fast,
lightweight system for multitasking that one might expect or hope for.
Threads are implemented in a way that make them easy to misuse. Few people
know how to use them correctly or will be able to provide help.

The use of interpreter-based threads in perl is officially discouraged.

You may want to look into doing this with multiple processes instead. A central manager process could take responsibility of handing out reasonably-sized chunks out to the workers. See for example fork or Parallel::ForkManager, as well as perlipc.

Its self-admitted FEARmongering from irc burnouts -- we're tired of trying to discourage folks from using threads and how to use threads on the irc .... lets scare them in the documentation .... it doesn't belong